Studying the consequences of hybridization on plant performance is insightful to understand the adaptive potential of populations, notably at local scales. Due to reduced effective recombination, predominantly selfing species are organized in highly homozygous multi-locus-genotypes (or lines) that accumulate genetic differentiation both among- and within-populations. This high level of homozygosity facilitates the dissection of the genetic basis of hybrid performance in highly selfing species, which gives insights into the mechanisms of reproductive isolation between lines. Here, we explored the fitness consequences of hybridization events between natural inbred lines of the predominantly selfing species Medicago truncatula, at both within- and among-populations scales. We found that hybridization has opposite effects pending on studied fitness proxies, with dry mass showing heterosis, and seed production showing outbreeding depression. Although we found significant patterns of heterosis and outbreeding depression, they did not differ significantly for within- compared to among-population crosses. Family-based analyses allowed us to determine that hybrid differentiation was mostly due to dominance and epistasis. Dominance and/or dominant epistatic interactions increased dry mass, while decreasing seed production, and recessive epistatic interactions mostly had a positive effect on both fitness proxies. Our results illustrate how genetic incompatibilities can accumulate at a very local scale among multi-locus-genotypes, and how non-additive genetic effects contribute to heterosis and outbreeding depression.

研究杂交对植物性能的影响对于了解种群的适应潜力，特别是在局部尺度上具有深刻的意义。由于有效重组减少，主要的自交物种被组织成高度纯合的多位点基因型（或系），在群体间和群体内积累遗传分化。这种高水平的纯合性有助于剖析高度自交物种中杂交性能的遗传基础，从而深入了解品系之间的生殖隔离机制。在这里，我们探讨了主要自交物种Medicago truncatula的自然近交系之间杂交事件的适应性后果，在人口内部和人口之间的规模。我们发现杂交对所研究的适应性代理具有相反的影响，干质量显示杂种优势，种子产量显示出远交衰退。尽管我们发现了显着的杂种优势和远交抑制模式，但它们在种群内杂交与种群间杂交中没有显着差异。基于家庭的分析使我们能够确定杂交分化主要是由于优势和上位性。显性和/或显性上位相互作用增加了干质量，同时减少了种子产量，而隐性上位相互作用对两种适应度代理都有积极影响。我们的结果说明了遗传不相容性如何在多位点基因型之间在非常局部的范围内积累，